Storing Info Between Events

ASPnoob

Hi all, Suppose I have a button in a windows form app that when clicked just once causes a text box to display one message, and when clicked twice causes the text box to display a different message. I have tried to use an if statement like the following to record the number of mouse clicks but it's not working. int clickCount=1; if (clickCount < 2) { txtDisplay.Text = txtDisplay.Text + "Side1"; clickCount++; } else { txtDisplay.Text = txtDisplay.Text + "Side2"; } It appears that each time the mouse is clicked, clickCount is set to 1 instead of having the value from the previous click. How do I store a value from the previous click event and use it in the current event? Please point me in the right direction, thanks in advance.

Lost User

You need to make clickCount a static variable so it is set to 1 at the beginning of the application.

speaking as ...

ignrod

Sorry to disagree with you, but this behavior of the static keyword corresponds to C++ and not C#. In fact, if you try to set a local variable ( i.e. defined inside a method ) as static in C#, you will obtain a compiler error. In my opinion, the best option to have clickCount record the number of clicks is to define it as a member variable and not a local one.

Lost User

ignrod wrote:

but this behavior of the static keyword corresponds to C++ and not C#.

Sorry to disagree with you but I guess you have not read this[^].

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Dave Kreskowiak

Sorry to disagree with you, but Richard is correct. Static variables work in C#.

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Luc Pattyn

Your code seems to suggest that you are maintaining the state of your app in a variable (clickCount) which is declared inside the button Click handler, which means it won't survive the handling of a click, hence it will always restart having the value of 1. You should move the declaration outside the method, i.e. make it a class member. That way, for each instance of the Form (assuming you might create more than one of them), the button would remember its state. You do not need the static keyword, unless you want to have all instances of that Form to share their state (which seems unlikely to me). IMO it is easier and robuster to put the state inside the button itself; there are several ways to achieve this; - one is to create your own MyButton class, inheriting from Button, and taking care of its peculiarities (IMO it would be overkill here); - another is to hide the state in the Tag property, which is a field provided but unused by Windows for all WinForms Controls, so it is available for whatever purpose you decide to use it for. Mind you, it is of type object, so you would need some casting. (I prefer this approach). - and then you could derive the state from existing variables and/or properties; in your example, you could perhaps just check the txtDisplay.Text and when it ends on "Side1" just replace "Side1" by "Side2". (I typically don't do it this way, as it is less robust; e.g. when you change languages, there is more code that needs changing). :)

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Luc Pattyn

Huh? when I try a static inside a method, I do get a compiler error (tried with .NET 2.0) It is the C++ doc, and not the C# doc (unfortunately), that says: When you declare a variable in a function, the static keyword specifies that the variable retains its state between calls to that function. :confused:

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ignrod

In fact, I have. If you have a look at the link you just posted, you will see a note in yellow color which says: "The static keyword has more limited uses than in C++. To compare with the C++ keyword, see Static (C++)." So, if you try the following code, it will not compile in C#

class ClickCount {

static void Main() {
	ClickCount click = new ClickCount();
	click.IncreaseClickCountByOne();
	click.IncreaseClickCountByOne();
	click.IncreaseClickCountByOne();
}

void IncreaseClickCountByOne() {
	static int clickCount = 1;
	clickCount = clickCount + 1;
	Console.WriteLine(clickCount);
}

}

Of course, member variables ( fields ) can be static or nonstatic. Any of them will keep their value between method calls.

class ClickCount {

static int clickCount = 1;

static void Main() {
	ClickCount click = new ClickCount();
	click.IncreaseClickCountByOne();
	click.IncreaseClickCountByOne();
	click.IncreaseClickCountByOne();
}

void IncreaseClickCountByOne() {
	clickCount = clickCount + 1;
	Console.WriteLine(clickCount);
}

}

class ClickCount {

int clickCount = 1;

static void Main() {
	ClickCount click = new ClickCount();
	click.IncreaseClickCountByOne();
	click.IncreaseClickCountByOne();
	click.IncreaseClickCountByOne();
}

void IncreaseClickCountByOne() {
	clickCount = clickCount + 1;
	Console.WriteLine(clickCount);
}

}

Both work exactly in the same way.

Lost User

Yes I agree, but that is not what I was suggesting.

speaking as ...

Lost User

Maybe I was not clear but I was talking about a static class variable.

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Luc Pattyn

As I can't get a local static to work in C# (as C/C++ would allow me to), I figured you meant a class member, but then I am puzzled as to why you want it to be static at all. And that is why I provided another answer to the OP, trying to state things more clearly. :)

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Lost User

Luc Pattyn wrote:

I am puzzled as to why you want it to be static at all

My C++ brain again ...

speaking as ...

Luc Pattyn

you should kickstart the brain that fits the forum. :-D

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Lost User

Even with a kick it's slow to react. :(

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Dave Kreskowiak

Same problem. I should have specified class scope statics.

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ASPnoob

Hi Luc, thanks for replying. I have searched for a way to "put the state inside the button itself" like you have suggested but all I've found were maintaining session state for web apps and not windows form apps. I'm also interested in your suggestion to "hide the state in the Tag property" but I can't find an example of how to do that either. Please give me links to articles on how to do those things I've just mention if you can. Thanks again for your help.

Dave Kreskowiak

What's so hard about it??

SomeButton.Tag = _stateValue_;

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Luc Pattyn

And the harder half of the job is getting the state back, which requires a cast as I said:

int myState=(int)myControl.Tag;

And no, I don't have a reference about this subject. Inheriting from a class, or creating a more specialized one, is a fundamental concept in Object-Oriented Programming. There are zillions of articles on the subject, why not try and read Custom Button - Issues with Focus Border, Text Color, etc.[^] (I didn't, it was the first I found using CP search). :)

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Luc Pattyn

(Sorry for a garbage sentence meant to fool the CP bugs and cache issues so I can get this posted) And the harder half of the job is getting the state back, which requires a cast as I said:

int myState=(int)myControl.Tag;

And no, I don't have a reference about this subject. Inheriting from a class, or creating a more specialized one, is a fundamental concept in Object-Oriented Programming. There are zillions of articles on the subject, why not try and read Custom Button - Issues with Focus Border, Text Color, etc.[^] (I didn't, it was the first I found using CP search). :)

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Luc Pattyn

(Another garbage sentence was needed to get this post accepted amidst bugs and cache issues, sorry for that) And the harder half of the job is getting the state back, which requires a cast as I said:

int myState=(int)myControl.Tag;

And no, I don't have a reference about this subject. Inheriting from a class, or creating a more specialized one, is a fundamental concept in Object-Oriented Programming. There are zillions of articles on the subject, why not try and read Custom Button - Issues with Focus Border, Text Color, etc.[^] (I didn't, it was the first I found using CP search). :)

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